The present invention relates to an electronic apparatus for the direct imprinting of color designs on stencils for screen-process printing by means of the electronic processing of the image which corresponds to the design to be printed and of the subsequent use of a beam of LASER rays to optically imprint the design on the textile support of the printing stencil.
As is known, the method currently most used for optically imprinting color designs on planar screen-process printing stencils entails, initially and in any case, the manual preparation of a color design by experts and then the creation, starting from said design, of a series of tracing sheets (or transparent films) whose number is equal to the number of colors of the design; the area which corresponds to a single color considered fundamental in that given design is defined in black on each of said tracing sheets or films. Accordingly, each black area of each transparent tracing sheet corresponds to a single fundamental color which will subsequently be used during printing in order to reproduce the original colored design.
These color areas can be partially superimposed so as to generate regions of a color which is the superimposition of one or more fundamental colors, thus allowing to keep the number of fundamental colors as small as possible. The images present on the tracing sheets are then transferred onto a support which allows to print them on fabric, i.e. a printing stencil. Said support is constituted by a rectangular frame, generally constructed by means of metallic profiled elements, over which a polyester fabric is stretched and glued. Said stencil is then impregnated with a particular light-sensitive gelatine and dried. Once dry, the printing stencil is optically imprinted by superimposing thereon one of said individual tracing sheets bearing the design to be transferred and by exposing the assembly to the light of a mercury-vapor lamp which contains a very intense ultraviolet component with an emission peak centered around 360 nm.
The part of gelatine which is struck by the ultraviolet light polymerizes and thus remains fixed to the supporting fabric, whereas the remaining part can be eliminated from the stencil by means of a simple wash with water.
In order to obtain a greater mechanical strength of the stencil during printing, said stencil is subsequently varnished, and the varnish which fills the design is removed by means of appropriate aspiration.
Due to the fact that during printing the fabric must generally be dried between the printing of one color and the printing of the next, it is evident that the production times (as well as the possible inaccuracies in the final result) decrease as the number of printed color overlays decreases, and therefore this justifies the need to reduce as much as possible the colors which can be considered fundamental for the forming of a given design.
An intermediate "tiling" step, i.e. a step in which the same area of the design is duplicated according to a given geometrical arrangement, may occur between the tracing and the related imprinting, with the purpose of completely filling the useful area of the printing stencil.
A manual "blending" operation, i.e. a modification of the outline of the design on the stencil so as to allow the best possible matching of the right and left sides of the image, which will have to match during printing, is often performed after imprinting.
Once the printing stencils have been obtained, the design is printed on fabric, using the colors considered most appropriate for each color overlay, thus acquiring the possibility of obtaining a plurality of "variations" of the same design. The person who selects the colors which must replace the original ones to print a given variation is always highly specialized.
This optical imprinting method, which comprises the manual preparation of the color design, the transfer of said design onto tracing sheets or transparent film and all the subsequent manual operations for reducing the number of fundamental colors and for adapting the size of the tracing sheets to the size of the support to be optically imprinted, in practice has problems and limitations which are mostly due to the need to perform a number of separate copies of the same design on tracing sheets which is equal to the number of colors considered fundamental, to the need to have highly specialized personnel available and to the considerable time required for the transfer of the original design onto tracing sheets, with evident high costs and low productivity.
In order to at least partially obviate these problems and the numerous manual interventions, various attempts have already been made to provide the process for the automatic imprinting of the textile support of a screen-process printing stencil starting from digital information, corresponding to the shape and color characteristics of the design to be printed, which can be processed by means of a computer so as to drive an ultraviolet light source in order to transfer the image of the design (or of parts thereof) onto the light-sensitive material spread on the support of the printing stencil.
However, in practice the imprinting method which uses digital information which can be processed on a computer has proved itself difficult to execute in practice and unsuitable for the optical imprinting of color designs on large supports.